Pyruvate kinase

Pyruvate Kinase is an enzyme involved in glycolysis, a metabolic pathway that plays a crucial role in the breakdown of glucose in cells. It catalyzes the transfer of a phosphate group from phosphoenolpyruvate (PEP) to adenosine diphosphate (ADP), yielding one molecule of pyruvate and one molecule of ATP.

Function

Pyruvate kinase is a key regulatory enzyme in the glycolytic pathway. It is the enzyme that catalyzes the final step of glycolysis, converting phosphoenolpyruvate (PEP) into pyruvate while simultaneously generating ATP from ADP. This reaction is exergonic and irreversible, which makes it one of the major regulatory steps of glycolysis.

Structure

Pyruvate kinase exists in two forms: a tetrameric form, which is found in the liver and is regulated by allosteric effectors, and a dimeric form, which is found in muscle and brain tissues and is not allosterically regulated. The enzyme is a protein made up of four identical subunits, each of which contains a binding site for PEP and ADP.

Regulation

The activity of pyruvate kinase is regulated by several mechanisms, including allosteric regulation, covalent modification, and gene expression. In the liver, the enzyme is inhibited by ATP and alanine, and activated by fructose 1,6-bisphosphate. In muscle and brain tissues, the enzyme is not allosterically regulated.

Clinical significance

Mutations in the gene encoding pyruvate kinase can lead to pyruvate kinase deficiency, a rare genetic disorder characterized by hemolytic anemia. In addition, the enzyme has been implicated in cancer metabolism, as cancer cells often exhibit increased glycolysis, a phenomenon known as the Warburg effect.

See also

• Glycolysis
• Enzyme
• Metabolism
• Pyruvate kinase deficiency
• Warburg effect